1. Field of the Invention
The present invention relates to a system and method for passing matter in a flow passage, in particular for passing trash or drill cuttings in a drilling fluid return line of an oil and/or gas drilling installation.
2. Background of the Invention
When drilling for oil and/or gas, a drilling fluid (e.g. drilling mud or seawater) is typically pumped from a drilling rig down the borehole to lubricate and cool the drill bit as well as to provide a means for removing drill cuttings from the borehole. After emerging from the drill bit, the drilling fluid flows up the borehole through the annulus formed by the drill string and the borehole.
In US2005/0092523 (McCaskill et al.), the flow of drilling fluid from the annulus passes upward through a casing, and exits the casing through laterally opening bell nipple. The exiting flow is conducted through a flowline to a choke or a choke manifold. Two chokes are associated with the choke manifold. Flow exiting from the choke or choke manifold is transported to a sump or mud pit via a return line.
The two chokes in US2005/0092523 are arranged in parallel. Typically, two chokes are used for redundancy, so that if one choke has to be taken out of service, the flow can be directed through the other choke.
However, a problem with the system in US2005/0092523, and other known systems, is that drill cuttings may clog the choke or choke manifold (or other valves or the like in a drilling fluid return line), which in turn negatively effects the performance of the system. The borehole bottom hole pressure will be impossible to maintain at a set value when clogging of the return line choke takes place.